Ocean on Saturn moon could be as salty as the Dead Sea

Jul 03, 2014 by Dwayne Brown
Researchers found that Titan's ice shell, which overlies a very salty ocean, varies in thickness around the moon, suggesting the crust is in the process of becoming rigid. Credit: NASA/JPL/SSI/Univ. of Arizona/G. Mitri/University of Nantes

(Phys.org) —Scientists analyzing data from NASA's Cassini mission have firm evidence the ocean inside Saturn's largest moon, Titan, might be as salty as the Earth's Dead Sea.

The new results come from a study of gravity and topography data collected during Cassini's repeated flybys of Titan during the past 10 years. Using the Cassini data, researchers presented a model structure for Titan, resulting in an improved understanding of the structure of the moon's outer ice shell. The findings are published in this week's edition of the journal Icarus.

"Titan continues to prove itself as an endlessly fascinating world, and with our long-lived Cassini spacecraft, we're unlocking new mysteries as fast as we solve old ones," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, who was not involved in the study.

Additional findings support previous indications the moon's icy shell is rigid and in the process of freezing solid. Researchers found that a relatively high density was required for Titan's in order to explain the gravity data. This indicates the ocean is probably an extremely salty brine of water mixed with dissolved salts likely composed of sulfur, sodium and potassium. The density indicated for this brine would give the ocean a salt content roughly equal to the saltiest bodies of water on Earth.

"This is an extremely salty ocean by Earth standards," said the paper's lead author, Giuseppe Mitri of the University of Nantes in France. "Knowing this may change the way we view this ocean as a possible abode for present-day life, but conditions might have been very different there in the past."

Cassini data also indicate the thickness of Titan's ice crust varies slightly from place to place. The researchers said this can best be explained if the moon's outer shell is stiff, as would be the case if the ocean were slowly crystalizing, and turning to ice. Otherwise, the moon's shape would tend to even itself out over time, like warm candle wax. This freezing process would have important implications for the habitability of Titan's ocean, as it would limit the ability of materials to exchange between the surface and the ocean.

A further consequence of a rigid ice shell, according to the study, is any outgassing of into Titan's atmosphere must happen at scattered "hot spots"—like the hot spot on Earth that gave rise to the Hawaiian Island chain. Titan's methane does not appear to result from convection or plate tectonics recycling its ice shell.

How methane gets into the moon's atmosphere has long been of great interest to researchers, as molecules of this gas are broken apart by sunlight on short geological timescales. Titan's present atmosphere contains about five percent methane. This means some process, thought to be geological in nature, must be replenishing the gas. The study indicates that whatever process is responsible, the restoration of Titan's methane is localized and intermittent.

"Our work suggests looking for signs of methane outgassing will be difficult with Cassini, and may require a future mission that can find localized methane sources," said Jonathan Lunine, a scientist on the Cassini mission at Cornell University, Ithaca, New York, and one of the paper's co-authors. "As on Mars, this is a challenging task."

Explore further: Cassini sheds light on Titan's second largest lake, Ligeia Mare

More information: Icarus, www.sciencedirect.com/science/… ii/S0019103514001444

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plaasjaapie
5 / 5 (1) Jul 03, 2014
If they have "firm evidence", why do they use "might"?
Torbjorn_Larsson_OM
5 / 5 (5) Jul 03, 2014
@plaasjaapie: Generally? Because observations have uncertainty.

Different areas come to a mutually agreed on quality level for tests, e.g. physicists may use 3 sigma for solid ("firm") theoretical evidence. (E.g. for observing the Higgs field they used 5 sigma, accounting for "look elsewhere" as they didn't know the exact free Higgs particle mass and looked at many masses before finding it.)

But even with the best evidence we can have, there will remain an uncertainty that the observation that looks like a signal in reality was due to random outcomes and/or contains systematic errors (calibrations, equipment errors, methodological errors, ...). That means scientists more often than not handles even "firm" evidence as it is, still with uncertainty. Especially if it needs repeats.

After many interconnecting observations secure a whole area, you see scientists drop "might". E.g. gravity exists, it doesn't "may" exist.

Here there was a saltiness range too, it may be less salty.
Torbjorn_Larsson_OM
5 / 5 (5) Jul 03, 2014
... or more salty, depending on how you parse the used language. (That's why you want to look at the paper, because the math description is not ambiguous like language is.)
malapropism
5 / 5 (2) Jul 03, 2014
If they have "firm evidence", why do they use "might"?

Presumably because the evidence is clear and unequivocal (the data from Cassini) but there could be different interpretations of (theories resulting from) the meaning of the data, none of which can be rejected with current knowledge but which are possibly mutually exclusive.
cantdrive85
1 / 5 (4) Jul 05, 2014
Researchers found that a relatively high density was required for Titan's ocean in order to explain the gravity data.


Possibly their understanding of gravity is skewed, being that many moons require subsurface water to explain their anomalous gravity data.